1. Field of the Invention
This invention relates to an elastomeric mounting/isolation system, especially a system for the undercarriage of a motor vehicle to isolate, or at least attenuate, the influence of certain road induced forces on the vehicle body.
2. Background Information
A known practice in the design and construction of motor vehicles is to mount the vehicle body on a frame or sub-frame of the vehicle chassis using an elastomeric mounting/isolation system that comprises several elastomeric mounting/isolation assemblies at appropriate locations. In the ensuing description, the word xe2x80x9cframexe2x80x9d will be used in a generic sense to denote any of various types of automotive vehicle frames.
One type of elastomeric mounting/isolation assembly comprises an annular elastomeric element, a rigid inner tubular sleeve, typically metal, passing concentrically through the elastomeric element, and a rigid outer tubular sleeve, also typically metal, within which the annular elastomeric element is concentrically disposed. An outer cylindrical surface of the annular elastomeric element joins with the inner cylindrical surface of the outer tubular sleeve in any suitable manner, such as by bonding of the elastomer to the sleeve. An inner cylindrical surface of the annular elastomeric element joins with the outer cylindrical surface of the inner tubular sleeve in any suitable manner, such as by bonding of the elastomer to the sleeve. The outer tubular sleeve is mounted on a vehicle frame in any suitable manner so as to be immovable on the frame The mounting may be accomplished by steps that include press-fitting the outer sleeve to an aperture of the frame.
The assembly further comprises: a second annular elastomeric element; a third annular elastomeric element; two rigid end caps, or end plates, which are typically metal; and a fastener. The inner tubular sleeve has an axial dimension sufficiently long that it protrudes in each of opposite axial directions beyond both the first annular elastomeric element and the outer tubular sleeve. Each end cap comprises a circular disk having a hole at its center. One end cap is disposed concentric with and against one end of the inner tubular sleeve while the other end cap is disposed concentric with and against the opposite end of that sleeve. The second elastomeric element is disposed concentric with both tubular sleeves and the first elastomericelement, but radially outward beyond the outer tubular sleeve, and between the frame and one of the end caps. The third elastomeric element is disposed concentric with both tubular sleeves and the first elastomeric element, but radially outward beyond the outer tubular sleeve, and between the frame and the other end cap. The other end cap is disposed to bear against a portion of the vehicle body.
The fastener, which may be a headed screw having a threaded shank, is used to fasten the assembly to the body. The screw shank passes through the one end cap, the inner tubular sleeve, the other end cap, and threads into a hole in the vehicle body. As the fastener is tightened by turning its head with a suitable fastening tool, the two end caps and inner tubular sleeve are immovably sandwiched together against the body, with the other end cap bearing directly against the body.
At the location where it mounts between the body and chassis, an elastomeric mounting/isolation assembly allows limited relative three-dimensional spatial motion between the frame and body. One dimension of motion is along the axis of the assembly. The other two dimensions are radial to the axis. The particular characteristics of the elastomers, such as dimensions, materials, durometers, etc., determine the ability of an assembly to perform its intended purpose of isolating and/or attenuating the influence of road-induced forces on the body. Those characteristics may be selected by mathematical and/or empirical analysis, in an effort to tune an assembly to produce a desired response in a particular application in a particular motor vehicle.
The construction of the assembly causes the characteristics of all three elastomeric elements to determine response of the assembly to certain types of relative motion. This inherent coupling of the elastomeric elements may impair the ability of an assembly to be tuned in a manner that best addresses both NVH (noise, vibration, harshness) and vehicle handling considerations. For example, a certain coupling exists between the radial and axial spring rates of the elastomeric elements. Changing elastomeric element characteristics to achieve a desired radial spring rate inherently affects axial spring rate, and vice versa.
As a result of the inventors"" recognition of these limitations on tuning such an assembly, they have conceived a novel and improved construction in which the elastomeric elements are effectively de-coupled such that changing one spring rate has substantially no effect on the other spring rate, and vice versa, or at least a significantly lesser effect than in the prior device described above. It is believed that this capability can enable an elastomeric isolator/mounting assembly to better meet diverse considerations involving NVH on the one hand and vehicle dynamics on the other.
Accordingly, a general aspect of the invention relates to an elastomeric mounting/isolation assembly for interfacing relatively movable members comprising a first annular elastomeric element, a rigid inner tubular sleeve disposed concentrically within the elastomeric element, and a rigid outer tubular sleeve within which the annular elastomeric element is concentrically disposed. The annular elastomeric element has an outer cylindrical surface joining with an inner cylindrical surface of the outer tubular sleeve and an inner cylindrical surface joining with an outer cylindrical surface of the inner tubular sleeve. A rigid end member that has a central through-hole aligned with the inner tubular sleeve is disposed axially beyond one of the two relatively movable members relative to the other of the two relatively movable members. A second elastomeric element is disposed radially outward beyond the outer tubular sleeve and axially between the one relatively movable member and the end member. A third elastomeric element is disposed radially outward beyond the outer tubular sleeve and axially between the two relatively movable members. A fastener, including a guide, fastens the end member and the other relatively movable member together, while disposing the guide within the inner tubular sleeve so that the inner tubular sleeve can slide axially along the guide, while causing the second elastomeric element to be held compressed between the end member and the one relatively movable member, and while causing the third elastomeric element to be held compressed between the two relatively movable members.
Another general aspect of the invention relates to an automotive vehicle having at least one assembly, as described in the preceding paragraph, mounting the vehicle body on the undercarriage.
Further aspects will be seen in various features of a presently preferred embodiment of the invention that will be described in detail and in principles of the invention as set forth in various claims.